Polyamide resins have excellent abrasion resistance, electrical properties, mechanical strength and chemical resistance. Therefore, their molded products have been used for various mechanical parts as engineering plastics. However, they have drawbacks such as large water absorbance, low impact resistance, particularly low notched impact strength. Further, they also have drawbacks that they are inferior in heat resistance under a high load or in moldability because they are crystalline resins.
Since the polyamide resins have such drawbacks, their use as engineering plastics is limited, and in some cases, their excellent properties can not be adequately utilized.
Among the conventional resin compositions composed of a polyamide resin and a styrene-type polymer, there has been no resin material which has not only excellent properties of both resins but also excellent impact resistance at a low temperature.
In this point of view, U.S. Pat. No. 4,987,185 to Aoki et al discloses a resin composition capable of providing a molded product having excellent heat resistance and impact resistance, particularly, remarkably improved impact resistance at a low temperature, by blending a certain specific copolymer containing an .alpha.,.beta.-unsaturated dicarboxylic anhydride monomer component to a resin mixture comprising a polyamide resin and a certain specific rubber-modified styrene graft copolymer.
The U.S. patent discloses an impact resistant thermoplastic resin composition having a notched Izod impact strength of at least 73 kg.cndot.cm/cm as measured at 23.degree. C. and a notched Izod impact strength of at least 44 kg.cndot.cm/cm as measured at -20.degree. C. As shown in FIG. 1 of the U.S. patent, the notched Izod impact strength is rapidly reduced below -20.degree. C.
U.S. Pat. No. 4,429,076 to Saito et al discloses a thermoplastic polymer composition comprising (a) a component A consisting of modified block copolymers and the ionically crosslinked products of the modified block copolymer with one metal ion, (b) a component B of polyamides, polyurethanes, vinylalcohol polymers, polyacrylates, polymethacrylates, chlorinated hydrocarbon polymers or ionomers, and optionally (c) styrene polymer and olefin polymer to improve processability. Although the polymer composition employs a modified block copolymer, the polymer composition is not for a polymer composition having excellent impact strength at low temperatures.
It is an object of the present invention to provide a resin composition capable of providing a molded article having remarkably improved impact strength at a low temperature to about -30.degree. C., by adding a hydrogenated block copolymer to which has been grafted by an unsaturated carboxylic acid or an unsaturated carboxylic anhydride, and an aromatic vinyl copolymer containing a maleimide together, to the base resin of the present invention.